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Wi-fi Physics

  1. Jan 8, 2006 #1
    As you know wi-fi is a radio signal and i'm wondering if physics can help me by determining why is my internet acting weird on me. I know about waves and nodes and antinodes and I'm wondering does wi-fi have these properties and how can i position it. In a geological perspective its distance from the router is about 15 meters and elevated by 2 meters (router=downstairs, upstairs=computer). What else can weaken the signal than its distance?

    p.s. I'm a techno student and everything about the computer is running good and i need some insight.
     
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  3. Jan 8, 2006 #2

    chroot

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    It won't be terribly useful to think about a Wi-Fi signal in terms of individual modes, as a Wi-Fi signal is spread-spectrum anyway. (The signal is composed of a large number of different frequencies in order to reject noise on any of them.)

    Radio signals, like wi-fi signals, will be attenuated by walls, metal objects, and so on. It's best to put the access point as high as possible and eliminate objects in the path between the wireless device and the access point.

    - Warren
     
  4. Jan 8, 2006 #3

    robphy

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    Noise and electromagnetic interference from other devices can also cause wi-fi problems... not to mention incorrect software settings.
     
  5. Jan 8, 2006 #4
    If you have a wireless phone that could also cause problems. I used to always get knocked off my wireless internet until I got a phone with a stronger signal. I'd like to know why it knocked me off though and why this one doesn't.
     
  6. Jan 9, 2006 #5

    berkeman

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    2.4GHz WiFi has several sub-bands, so maybe it's on a different sub-band compared to your PC. For the OP, the biggest interfence sources are microwave ovens and other WiFi installations. If you have a neighbor with wireless devices, that can cause flaky RF problems, especially if they are using a WiFi router and doing file transfers. The multi-floor configuration can also be a problem, depending on the building materials used between floors. The nulls from multipath are definitely a problem, with many 10's of dB of signal loss in the nulls. The pesky nulls for 2.4GHz WiFi are on the order of a couple cm across, so they can be a real pest. They also are time variant, since the human body absorbs 2.4GHz RF so well (that's why microwave ovens use the 2.4GHz band to cook food), so people moving around will modulate the position and depth of the nulls. If your base station has two antennas for "spatial diversity", then that's about as good as you can get with standard WiFi.
     
  7. Jan 9, 2006 #6

    russ_watters

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    Masonary walls, especially, are a real killer. I live in a split-level condo with concrete floors/ceilings and the wet wall in the middle, making for an S-curve up a half-level of stairs from my router to my bedroom. I have to aim the signal into the hallway, using it as kinda a wave-guide. Still, I needed a high-end router to get consistent signals in my room.
     
  8. Jan 9, 2006 #7
    I have 2.4 phones and noticed people in the surrounding area have Wireless internet. Could there be any more Obstructions and what materials can I use to improve my connection to the internet?
     
  9. Jan 9, 2006 #8

    berkeman

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    I wish I had 2.4 phones.... :-) About the only things you can try are to experiment with different channel settings (or talk to your neighbors to actively spread the channels around among nearest neighbors), and to do like Russ said and try to aim your router up the stairs. If you can set up a reflector at the top of the stairs and aim it at your PC (and sit behind the PC, not between the reflector and the PC), that has a chance of improving your reception. Also be sure to check out the received signal strength meter at your PC, to see if it helps you do the aiming. When microwave ovens get used nearby, that's still going to temporarily mess up the received signal.

    If you wanted to get real fancy (and not exactly comply with the FCC guidelines for the ISM band), you could use a directional antenna at the router and experiment with aiming it upstairs. You could really blast the upstairs (at the expense of everywhere else) with a good directional antenna and a standard WiFi router.....:devil:
     
  10. Jan 16, 2006 #9
    If I put one end of a wire next to my wireless router and the other end near my wireless adapter, would I increase the strength?
     
  11. Jan 16, 2006 #10

    berkeman

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    Probably not, but you're thinking along the same lines as me when I suggested using a directional antenna. A little better than your wire would be to remote the router antenna with a length of coax, but that introduces coax losses and SWR issues. How many locations in your place do you want to be good hot spots?
     
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